PROJECT SUMMARY We will develop and commercialize to the research community a new class of glycan-specific binding reagents that incorporate the recognition function of variable lymphocyte receptors (?VLRs?), the antigen receptors of the adaptive immune system of jawless vertebrates, lamprey and hagfish. Such reagents are essential to detecting, localizing, quantifying, and establishing biological function(s) of specific glycans in normal and disease cells and tissues, and may additionally lead to development of new diagnostic and therapeutic modalities. The current absence of such reagents is a significant barrier to further advancing an understanding the role of glycans in health and disease. VLRs are composed of tandemly arranged highly diverse leucine-rich repeat (LRR) structural motifs with diversity comparable to the human immunoglobulin (Ig) antibody repertoire, and possess a distinctive more rigid binding site geometry vs Ig antibodies that is entirely contained within a single polypeptide structure. Vertebrates split into jawless and jawed vertebrate lineages approximately 550 million years ago. The evolutionary separation of jawless vertebrates from humans and other mammals, and the distinctive binding site geometry of VLRs potentially provide novel specificities and functions not accessed with Ig antibodies. This expectation is supported by the discovery of VLRs that bind carbohydrate antigens with affinity and specificity superior to that typically achieved with Ig antibodies and indicate that VLRs are uniquely well-suited to binding and discriminating glycan structures. The lamprey VLR-based immune system is potentially a transformative technology for the rapid, high throughput production of specific binding reagents for the diverse glycan structures that comprise the human glycome. With this phase 1 STTR application we will initiate this application of the lamprey VLR-based immune system by demonstrating that lamprey can be immunized to produce VLRs that specifically bind and discriminate each of the four most common mucin-type O-linked glycan core structures in humans. In our follow-on phase 2 studies we will express these VLRs in a form that facilitates use for detecting, quantifying and modulating the functions of the four mucin-type O-linked glycan core structures and provide these reagents to the research community.